[ILUG] Highpoint Sata RAID

[Gareth Eason]

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	Growing an array has been discussed on list before. the short answer is
either use LVM (and not RAID - or RAID1) or forget it. Growing the
filesystem is easy - growing a RAID5 / RAID6 array is not practical.
RAID4 can be grown, but is generally not supported except on high-end
storage systems (where you DO need to throw more disk in, grow a
filesystem and carry on without down-time. See NetApp's WAFL for an
example of this.)

	I'm open to correction on this, of course - and further developments
may mean that what's impractical on Linux today becomes the 'done thing'
tomorrow :-)

	Hope this helps.
	Best regards,
	-->Gar


John Coleman wrote:
| On Fri, 25 Mar 2005 13:58:20 +0000, Niall O Broin <niall at linux.ie> wrote:
|
|>On 25 Mar 2005, at 13:00, John Coleman wrote:
|>
|>
|>>With whichever card I buy, I'm going to be putting 3x 400Gig drives in
|>>them as one raid5 array, single logical drive, formatted with XFS. I
|>>intend to expand this array with more drives down the road but I have
|>>a query regarding the array expansion; after plugging in the new
|>>drive, I expect the controller to intergrate the drive into the
|>>current array, and that the existing logical drive will need to be
|>>increased to take advantage of the new space offered.
|>>I have 2 concerns regarding this:
|>>Firstly, ignoring downtime, will the existing partition on the logical
|>>drive remain untouched, with the additional space showing up as
|>>unpartitioned dirive space?
|>>Secondly, I have never had to change the size of a partition where the
|>>data was critical, I assume there are methods in place to expand the
|>>existing partition to use the whole logical drive, and that XFS
|>>supports expansion in such a way?
|>
|>XFS does indeed support expanding a filesystem, with the xfs_growfs
|>command. The xfs expansion will be the least of your problems. You need
|>to do the following:
|>
|>1) Add the extra disk into the RAID-5 array.
|>2) Increase the size of the partition on which the filesystem lives.
|>3) Extend the filesystem.
|>
|>Getting the easy stuff out of the way first, 3) is supported by
|>xfs_growfs.
|>
|>2) is a bit of a mess, because you have a disk which has a partition
|>table, and suddenly that partition table is wrong and needs changing.
|>I've done this on raw disks, and it has worked, and it has failed. LVM
|>may be of some help here - a little light reading might be in order :-)
|>
|
| I'd an idea LVM might have to be involved.
|
|>1) is where Aughrim may be lost. IIRC we had this discussion here a
|>while ago. With any RAID cards I have used, adding an extra drive into
|>the array means rebuilding the array (because data is striped across
|>all disks).
|
|
|>However, I'm pretty sure that somebody on the list
|>mentioned some cards which have some magic means of doing just this. A
|>search of the archives might help (I tried, but my google foo is weak).
|
| I'm fairly sure that the LSI card can do it without losing data.
|>From my (albeit totally theoretical) understanding, the 3ware and LSI
| cards array model looks something like this:
| drives on card -> card configures drives into array(s) -> card creates
| logical disks on each array -> partition is created on the logical
| disk by OS -> partition is formatted by OS
|
| Now, where I can see a problem is in the logical disk on which the
| partition-table resides suddenly becoming bigger after the card has
| incorporated the new disk into the given array.
| Surely this is similar to putting a ghost image on a drive which is
| larger than the image? The partition table should update (possibly
| through some utility? cfdisk?), then use another utility (xfs_growfs?)
| to expand the partition/format the free space?
|
| This part is crucial, otherwise it'll be another while before I get
| this array built as I can only afford 3 drives at the moment, but I
| plan on having 6-8 (maybe with one as a hot-spare) in the end.
|
|>Last but not least - you mentioned critical data. It'd take a much
|>braver man than me to try to do this with valuable data which is not
|>safely backed up.
|>
|>Niall
|>
|>--
|>Irish Linux Users' Group
|>http://www.linux.ie/mailman/listinfo/ilug/
|>
|>
|
| OT: fakeraid cards are dirty hacks, utterly deplorable. They are only
| helping to breed confusion and disinformation amongst consumers who
| believe they have a fast/secure raid setup.
| An IDE controller lashing together two drives in a container does not
| a RAID controller make.
|
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